I would be surprised if comments had much to do with this.
Google analytics tells you exactly everything you need to know about the visitors to a webpage.
Google adsense will control what ads you see or else an advertiser will do a deal directly with a website to advertise on specific pages.
They really do. I had a website. Google adsense is only one advertiser, there are others to choose from. I used wordpress as advertiser and would get approached by smaller advertisers giving me offers and asking me to prove how successful my site is.
Google analytics stats are a private thing between site owner and Google. Site owner can tell the advertiser or screenshot their stats, but there is no way to prove it. They could be lying or photoshopping. Google doesn't want to help with that because they don't want to share their data with competition.
So when you enter into negotations you use things like comments which are visible to third party.
If one is a big client, which I assume Mail Online is, they can even attempt to get google to pay them per view instead of per click. Or renegotiate price based on offer from other advertisers.
Then there is more technical details, like Google measures time spent on page when deciding how to rank it in SERP and leaving a comment takes time.
I am not saying it makes a huge difference, I mean there are sites that don't even have option to comment, but it does matter some.